1. Field of the Invention
The present invention relates to a control system for a vehicle component such as a vehicle power train, more specifically, it relates to an integrated control system for vehicle power train components including an engine and a transmission.
2. Description of Related Art
An integrated control system for vehicles is disclosed in JP-A-07-108882 and JP-A-05-85228. In such the integrated control system, a plurality of control units are arranged in upper and lower layers, and the control unit in the upper layer supervises and commands the control unit in the lower layer. For example, a main power train control unit controls a fuel injection control unit, an ignition control unit, an input and output control unit, a transmission control unit and a throttle control unit via a communication line. In such an integrated system, the control unit in the upper layer computes a command signal for the control unit in the lower layer. However, the control unit in the lower layer might not be able to respond to the command signal due to its control characteristics.
For example, consider the case where a main control unit and an engine control unit are connected via a communication line, the main control unit computes a target engine torque, and the engine control unit controls the engine in accordance with the target engine torque. Since the target engine torque is only computed, in particular cases, the engine cannot actually output the target engine torque. For example, in a particular small torque range, the engine torque may be controlled in a step-by-step manner, and there is a range in which the target engine torque is not available. As a result, the vehicle may be driven and operated in an undesirable manner.